Diaphragm for loud speakers



Nov. 22, 1932. D. c. A. HULTSTRCM DIAPHRAGM FOR LOUD SPEAKERS Filed Sept. 29, 1931 Patented Nov. 22, 1932 UNITED STATES DAVID CARL ALFRED HULTSTRtjM, OF BERLIN, GERMANY DIAIHRAGM FOR LOUD SPEAKERS Application filed September 29, 1931, Serial No. 565,887, and in Germany March 14, 1930.

This invention relates to a diaphragm for loud speakers in the form of a trough, of part cylindrical shape for example, open or r closed at the ends.

According to the invention the diaphragm is stiffened by at least one internal or external rib extending across the curved surface of the trough transversely to the longitudinal direction thereof. Owing to the construction corresponding to this invention a loud reproduction of notes of any pitch is obtained. Objectionable subsidiary vibrations are prevented. The diaphragm according to the 1nvention can be made of particularly large area, since the vibrations therein are transmitted uniformly to all parts of the diap-hragm.

Various constructional forms of the invention are illustrated by way of example in th accompanying drawing, in which Figure 1 shows a cross section through one constructional form,

Figure 2 a plan of this constructional form.

Figure 3 shows a cross section through a modified constructional form.

Figure 4 a cross section through a third constructional form, and

Figure 5 a section on the line V-V in Figure 4 on a larger scale for greater stiffness.

In the constructional form illustrated in Figures 1 and 2, the diaphragm a which has the shape of a segment of a cylinder, is secured in a box 7), by means of clamping strips 0 and screws d. The clamping strips press plane extensions a, of the trough shaped diaphragm against rims e on the box Z).

Portions of the side walls of the box 5 are thickened and felt strips f are secured to such thickened portions upon which bear the end margins of the diaphragm, which do not touch the side walls of the box. The diaphragm a is provided with a high rib g, which extends over it transversely. The rib may consist for example of plywood. It is essential that it should be light and sufficiently stifi. To the rib is secured the control needle h for the diaphragm. An example of a method of fastening the needle will be further described with reference to Figure 5.

It is essential that the diaphragm should be smooth, that is to say, not pleated or rib bed, in order that the cylindrical trough shape, in co-operation with the rib, may yield a satisfactory stiffening of the diaphragm, thus ensuring a satisfactory propagation of the oscillations right to the outermost edges of the diaphragm. It is also important that by the method of securing the diaphragm an alteration in the length of the chord of the cylindrical segment under the influence of the oscillations should be guarded against, even at the parts of the diaphragm farthest away from the rib.

In the constructional form according to P F lgure 3 the outer flat portions of the dia- U phragm serving for fastening it to the box are connected with the trough shaped portion by curved transitions.

Instead of the felt support there may be secured to the end walls of the box Z), opposite to the lateral edges of the diaphragm, strips of cloth or the like, which serve the same purpose as the felt strips f in the constructional form according to Figures 1 and 2, that is to say, they are intended to guard against scraping noise when the diaphragm is vibrating. The cloth strips might alternatively be secured to the edge of the diaphragm. Instead of being lodged in a box, the diaphragm might be arranged behind a sounding wall or might even be free.

Instead of the circular trough shaped form shown, some other trough shaped form, an elliptical one for instance, might be chosen. The diaphragm might even be of such a shape that its radius of curvature varies in a periphoral or in a longitudinal direction.

While in the constructional forms according to Figures 1 and 2, or in that according to Figure 3, the rib g is secured to the convex side of the diaphragm, in the constructional form according to Figure 4 it is secured to the concave side. Furthermore in the constructional form according to Figure 4, the thin rib is reinforced at its edges, that is, at for instance by applying ply-wood frames.

Moreover in some constructional forms the rib might be formed with apertures for the purpose of diminishing its weight and therefore its inertia.

In Figure 5 the method of securing the control needle k is illustrated. A screwthreaded extension k on the control needle goes through a bore in the reinforced margin 9 of the rib. In the adjacent thin portion of the rib 9, close to the thickened margin 9 is formed a transverse bore 2', in which is arranged a nut is screwed on to the extension k The edges of the reinforced margin 9 are capped by small U-shaped sheet-metal clips, in order to present a good bearing surface for the nut is and for a collar m provided on the needle h.

I claim 1. A diaphragm for loud speakers, comprising a trough-shaped body curved in section, and at least one stiffening rib extending in the peripheral direction about the curved surface of the body and disposed transversely to the longitudinal direction of the latter.

2. A diaphragm for loud speakers, comprising a trough-shaped body partly cylindrical in section, and at least one stiffening rib extending in the peripheral direction about the curved surface of the body and disposed transversely to the longitudinal direction of the latter.

3. A diaphragm for loud speakers, comprising a trough-shaped body curved in section and having open ends, and at least one stiffening rib extending in the peripheral direction about the curved surface of the body and disposed transversely to the longitudinaldirection of the latter.

4. A diaphragm for loud speakers, comprising a trough-shaped body partly cylindrical in section and having open ends, and at least one stiffening rib extending in the peripheral direction about the curved surface of the body and disposed transversely to the longitudinal direction of the latter.

In testimony whereof I aflix my signature.

DAVID CARL ALFRED HULTSTROM. 

